U.S. patent number 5,895,332 [Application Number 08/864,502] was granted by the patent office on 1999-04-20 for chain tensioning apparatus for a packaging machine.
This patent grant is currently assigned to Riverwood International Corporation. Invention is credited to Gerald J. Geisenhof, Allen L. Olson.
United States Patent |
5,895,332 |
Olson , et al. |
April 20, 1999 |
Chain tensioning apparatus for a packaging machine
Abstract
A tensioning system for an endless chain comprising a snail cam
mounted on a second shaft parallel to a sprocket shaft which
supports a sprocket and chain, a follower running against the snail
cam and mounted on a mechanism supporting the sprocket shaft, a
ratchet device which selectively limits the rotational direction of
the second shaft so that the radius of the snail cam at the
follower increases with rotation, a means of applying a controlled
rotational force to the second shaft to advance the ratchet device
if chain tension is below a predetermined level, but not advance it
if chain tension is above a predetermined level.
Inventors: |
Olson; Allen L. (Crosby,
MN), Geisenhof; Gerald J. (Ft. Ripley, MN) |
Assignee: |
Riverwood International
Corporation (Atlanta, GA)
|
Family
ID: |
21789779 |
Appl.
No.: |
08/864,502 |
Filed: |
May 29, 1997 |
Current U.S.
Class: |
474/113; 198/813;
74/128; 474/101; 474/136; 474/110 |
Current CPC
Class: |
F16H
7/1263 (20130101); B65G 23/44 (20130101); F16H
7/14 (20130101); Y10T 74/1529 (20150115); F16H
2007/0891 (20130101) |
Current International
Class: |
F16H
7/12 (20060101); F16H 7/08 (20060101); F16H
007/14 () |
Field of
Search: |
;474/101,103,104,105,110,136,114,113 ;198/813,814
;74/128,126,141.5,142 ;248/657,658 ;340/686,668,676 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Marmor; Charles A.
Assistant Examiner: Parekh; Ankur
Attorney, Agent or Firm: Skinner and Associates McLary;
Steve
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit, under 35 U.S.C. 119(e), of
U.S. provisional application Serial No. 60/018,786, filed May 31,
1996.
Claims
What is claimed is:
1. An apparatus for tensioning an endless drive means,
comprising:
(a) a first shaft which supports at least one endless drive
means;
(b) a support mechanism supporting said first shaft, said support
mechanism being movable in a direction normal to said first
shaft;
(c) a second shaft disposed parallel to said first shaft;
(d) a snail cam connected to said second shaft and having an outer
surface with an increasing radius;
(e) a follower connected to said support mechanism, said follower
being communicatively disposed against said outer surface of said
cam;
(f) means for selectively limiting rotational direction of said
second shaft; and
(g) a means of applying a rotational force to said second
shaft.
2. The apparatus of claim 1, wherein said endless drive means is a
chain.
3. The apparatus of claim 2, wherein said first shaft has a
sprocket supporting said chain.
4. The apparatus of claim 1, wherein said support mechanism is a
slide.
5. The apparatus of claim 1, wherein said snail cam is a plate.
6. The apparatus of claim 1, wherein rotation of said second shaft
is selectively limited to a direction in which said radius of said
outer surface of said cam at said follower increases with
rotation.
7. The apparatus of claim 1, wherein said means for selectively
limiting rotational direction of said second shaft is a ratchet
device.
8. The apparatus of claim 7 wherein said ratchet device has a
mechanism for selecting said rotational direction of said second
shaft.
9. The apparatus of claim 8, wherein said mechanism for selecting
said rotational direction of said second shaft limits rotation of
said second shaft in either a first direction or a second
direction.
10. The apparatus of claim 8, wherein said mechanism for selecting
said rotational direction of said second shaft is remotely
actuated.
11. The apparatus of claim 7, wherein said ratchet device can lock
said second shaft to prevent its rotation.
12. The apparatus of claim 1, wherein said means of applying a
rotational force to said second shaft includes a lever arm, a
one-way clutch connected to and acting between said second shaft
and said lever arm, and means for moving said lever arm.
13. The apparatus of claim 12, wherein said means for moving said
lever arm is a pneumatic cylinder.
14. The apparatus of claim 12, wherein said means for moving said
lever arm is a hydraulic cylinder.
15. The apparatus of claim 1, wherein said rotational force is a
controlled force whereby said means for selectively limiting
rotational direction of said second shaft advances if tension in
said at least one endless drive means is below a predetermined
level, but does not advance if tension in said at least one endless
drive means is above a predetermined level.
16. The apparatus of claim 1, further comprising a sensor which
detects a predetermined travel limit of said support mechanism when
said at least one endless drive means has been stretched a
predetermined amount.
17. The apparatus of claim 16, wherein said sensor sends a signal
to prevent operation of a machine on which said at least one
endless drive means is used.
18. An apparatus for tensioning an endless drive means,
comprising:
(a) a frame;
(b) at least one slide mechanism having a stationary portion
attached to said frame and a moveable portion sliding on said
stationary portion;
(c) a support structure attached to said moveable portion of said
slide mechanism;
(d) a rotatable first shaft supported by said support structure on
said at least one slide mechanism, said at least one slide
mechanism oriented to facilitate motion of said support structure
in a direction normal to said first shaft;
(e) at least one endless drive means supported by said first
shaft;
(f) a rotatable second shaft oriented parallel to said first, said
second shaft supported by said frame;
(g) at least one snail cam attached to said second shaft, said
snail cam having an outer surface with an increasing radius;
(h) at least one follower connected to said support structure, said
follower engaging said outer surface of said snail cam;
(i) a ratchet device operating between said frame and said second
shaft, said ratchet device selectively limiting rotational
direction of said second shaft to a direction in which said radius
of said outer surface of said cam at said follower increases with
rotation of said second shaft;
(j) a lever arm rotatably attached to said second shaft;
(k) a one way clutch connected to and operating between said lever
arm and said second shaft, said one way clutch allowing said lever
arm to rotate in only one direction on said second shaft; and
(l) means for applying a controlled force to said lever arm;
whereby said means for applying a controlled force to said lever
arm causes said lever arm to rotate in a direction that causes said
one way clutch to engage said second shaft so that said second
shaft rotates with said lever arm, thereby rotating said snail cam
to thereby move said support structure in a direction that tensions
said at least one drive means.
19. An apparatus for tensioning an endless chain on a machine,
comprising:
(a) a frame;
(b) at least one slide mechanism having a stationary portion
attached to said frame and a moveable portion sliding on said
stationary portion;
(c) a sensor which detects a predetermined travel limit of said
slide mechanism when said at least one chain has been stretched a
predetermined amount, said sensor sending a signal to prevent
operation of the machine;
(c) a support structure attached to said moveable portion of said
slide mechanism;
(d) a rotatable sprocket shaft supported by said support structure
on said at least one slide mechanism, said at least one slide
mechanism oriented to facilitate motion of said support structure
in a direction normal to said sprocket shaft;
(e) at least one sprocket attached to said sprocket shaft;
(f) at least one endless chain running on said at least one
sprocket;
(g) a rotatable second shaft oriented parallel to said sprocket
shaft, said second shaft supported by said frame;
(h) at least one snail cam attached to said second shaft, said
snail cam having an outer surface with an increasing radius;
(i) at least one follower connected to said support structure, said
follower engaging said outer surface of said snail cam;
(j) a ratchet device operating between said frame and said second
shaft, said ratchet device having a mechanism for selectively
limiting rotational direction of said second shaft to a direction
in which said radius of said outer surface of said cam at said
follower increases with rotation of said second shaft;
(k) a lever arm rotatably attached to said second shaft;
(l) a one way clutch connected to and operating between said lever
arm and said second shaft, said one way clutch allowing said lever
arm to rotate in only one direction on said second shaft; and
(m) a pneumatic cylinder connected between said lever arm and said
frame, whereby said pneumatic cylinder causes said lever arm to
rotate in a direction that causes said one way clutch to engage
said second shaft so that said second shaft rotates with said lever
arm, thereby rotating said snail cam to thereby move said support
structure with said sprocket shaft and said at least one sprocket
in a direction that tensions said at least one chain.
20. An apparatus for tensioning an endless drive means,
comprising:
(a) a first shaft which supports at least one endless drive
means;
(b) a support mechanism supporting said first shaft, said support
mechanism being movable in a direction normal to said first
shaft;
(c) a second shaft disposed parallel to said first shaft;
(d) a cam connected to said second shaft;
(e) a follower connected to said support mechanism, said follower
being communicatively disposed against said cam;
(f) a ratchet device for selectively limiting rotational direction
of said second shaft; and
(g) a means of applying a rotational force to said second
shaft.
21. An apparatus for tensioning an endless drive means,
comprising:
(a) a first shaft which supports at least one endless drive
means,
(b) a support mechanism supporting said first shaft, said support
mechanism being movable in a direction normal to said first
shaft;
(c) a second shaft disposed parallel to said first shaft;
(d) a cam connected to said second shaft;
(e) a follower connected to said support mechanism, said follower
being communicatively disposed against said cam,
(f) means for selectively limiting rotational direction of said
second shaft; and
(g) a means of applying a rotational force to said second shaft,
said means of applying including a lever arm, a one-way clutch
connected to and acting between said second shaft and said lever
arm, and means for moving said lever arm.
22. An apparatus for tensioning an endless drive means,
comprising:
(a) a first shaft which supports at least one endless drive
means;
(b) a support mechanism supporting said first shaft, said support
mechanism being movable in a direction normal to said first
shaft;
(c) a second shaft disposed parallel to said first shaft;
(d) a cam connected to said second shaft;
(e) a follower connected to said support mechanism, said follower
being communicatively disposed against said cam;
(f) means for selectively limiting rotational direction of said
second shaft; and
(g) a means of applying a rotational force to said second shaft,
wherein said rotational force is a controlled force, whereby said
means for selectively limiting rotational direction of said second
shaft advances if tension in said at least one endless drive means
is below a predetermined level, but does not advance if tension in
said at least one endless drive means is above a predetermined
level.
23. An apparatus for tensioning an endless drive means,
comprising:
(a) a first shaft which supports at least one endless drive
means;
(b) a support mechanism supporting said first shaft, said support
mechanism being movable in a direction normal to said first
shaft;
(c) a second shaft disposed parallel to said first shaft;
(d) a cam connected to said second shaft;
(e) a follower connected to said support mechanism, said follower
being communicatively disposed against said cam;
(f) means for selectively limiting rotational direction of said
second shaft;
(g) a means of applying a rotational force to said second shaft;
and
(h) a sensor which detects a predetermined travel limit of said
support mechanism when said at least one endless drive means has
been stretched a predetermined amount.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to chain-utilizing
machinery. More particularly, the invention relates to automated
packaging machinery which utilize chains in drive conveyors and
other assemblies or mechanisms thereof. However, the invention also
may be found to have utility in other applications.
2. Background Information
Endless means such as chains, belts, cables and ropes have many
uses on machinery. For example, torque is transferred from one
rotating element to another through endless means running on
shafts, pulleys or sprockets. Processing conveyors often are driven
by endless means and may have conveyor elements attached to the
endless means. Endless means stretch with use over time, and proper
tension must be maintained in the endless means for the machinery
to properly operate. The invention is described with respect to a
chain, specifically a chain-driven conveyor, but the invention is
applicable to tensioning other endless means.
One type of machine which commonly uses chain driven conveyors is a
packaging machine. In a typical packaging machine for placing
groups of articles, such as bottles or cans, within individual
cartons, the cartons are in a collapsed form, called a blank, at
one end of the packaging machine. Articles to be packaged are also
fed in mass into one end of the machine. The machine opens a carton
blank, groups and positions articles to be placed in the carton;
brings the group of articles and carton together; then closes and
seals the carton, and dispenses it out the other end of the
machine.
The continuous motion of all the articles, cartons, packaged
articles and mechanisms of the packaging machine is synchronized by
mechanical and electronic devices. One of the most common
mechanical devices used is a continuous chain. A typical packaging
machine will have a number of continuous chains each performing a
different function, and each with different elements attached to
it. Such elements include flight bars for separating articles into
groups, conveyor members for moving articles, pop-up conveyor
members for maintaining separation of grouped articles, lugs and
carrier assemblies for moving cartons, and barrel cam cross loading
mechanisms for pushing grouped articles into cartons. All of these
chains must be maintained at the proper tension for the machine to
properly function. As the machine is used over time, the pins and
holes of the chain wear causing the chains to stretch and lose
tension. Consequently, each chain must be periodically
retensioned.
In the past, chain tensioning has been done manually using a wrench
or lever turning a series of screws, shafts, or turnbuckles. The
tension developed in the chain was subject to the skill of the
person tensioning it, and often varied depending on the strength of
the person making the adjustment and the size of the wrench used.
Too high a tension creates unnecessary wear of the chain, and too
low of a tension may allow too much movement of the chain and
potential disaster if a chain were to come off a sprocket.
Despite the need in the art for a chain tensioning system which
overcomes the disadvantages, shortcomings and limitations of the
prior art, none insofar as is known has been developed.
Accordingly, it is an object of the present invention to provide an
improved chain tensioning system which more accurately controls the
level of tension in a chain. It is a further object of this
invention to provide a chain tensioning system which is less
dependent on the skill of the person adjusting the tension to
achieve the proper tension. It is a further object of this
invention to provide a chain tensioning system which indicates when
a chain has been stretched to its limit and prevents the machine
from operating. It is a further object of this invention to provide
a chain tensioning system which tensions a chain
semi-automatically.
BRIEF SUMMARY OF THE INVENTION
The apparatus of the present invention provides a chain tensioning
system for a chain used, for example, on a packaging machine
wherein the chain tensioning system provides tension to the chain
incrementally as controlled by a ratchet device. A controlled
force, such as that applied by a pneumatic cylinder, is applied to
the ratchet device periodically, such as at the start of each day.
If the chain is loose enough to allow the controlled force to
advance the ratchet device at least one step, then the ratchet
advances and holds the chain at a higher tension level when the
controlled force is removed. If the controlled force is
insufficient to advance the ratchet device one step, then the
ratchet device does not advance, and the ratchet device holds the
chain at the previous tension level when the controlled force is
removed. Tensioning the chain is thereby a semi-automatic operation
requiring a machine operator to only activate a device which
applies the controlled force. The system then sets proper tension
in the chain.
The chain tensioning system includes a device, such as a pneumatic
or hydraulic cylinder, for applying and releasing a controlled
force which acts on a lever arm connected to a one-way clutch or
bearing, which rotates a shaft connected to the input of the
ratchet device. The one-way clutch or bearing allows the
reciprocating linear motion of a device such as a pneumatic
cylinder to drive the ratchet device in one rotational direction.
The ratchet device may have gears or other mechanisms to ratio the
out put of the device to the input. The rotational output of the
ratchet device is attached to a snail cam on which rides a cam
follower attached to a movable structure supporting the shaft and
sprockets on which the chain travels. As the output of the ratchet
device rotates the snail cam, the snail cam moves the cam follower
which pushes the movable structure, typically on slide tracks, to
tighten the chain. The tension imparted on the chain is dependent
on the amount of controlled force imparted by the pneumatic
cylinder and the size of the incremental force needed to advance
the ratchet device.
The present invention also includes a safety device that prevents
the chain from being stretched beyond its safe limit. A sensor such
as a proximity sensor is positioned to detect a feature of the
movable structure on which the sprockets are mounted. If the
tensioning operation causes the chain to stretch beyond a defined
limit, the feature will be with the sensing range of the sensor,
and the sensor will then signal the machine controller and prevent
the machine from operating.
The features, benefits and objects of this invention will become
clear to those skilled in the art by reference to the following
description, claims and drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a side view of a packaging machine using a chain
tensioner of the present invention.
FIG. 2 is a detailed side view of area 2--2 of FIG. 1 showing the
chain driven carton placing mechanism which uses an embodiment of
the chain tensioner of the present invention.
FIG. 3 is a detailed side view of the area 3--3 of FIG. 2 showing
the mechanisms of an embodiment of the chain tensioner.
FIG. 4 is a top view of the mechanisms shown in FIG. 3.
FIG. 5 is a side view of the ratchet mechanism shown in FIGS. 3 and
4.
FIG. 6 is a perspective view of another embodiment of the chain
tensioner of the present invention.
FIG. 7 is a top view of the mechanisms shown in FIG. 6.
FIG. 8 is an exploded view of the mechanisms shown in FIG. 6.
DETAILED DESCRIPTION
Industrial process equipment often operates using endless chains to
drive conveyors or other mechanisms for processing items. The
present invention provides a mechanism for tensioning endless
chains on such equipment in an easy, repeatable, reliable manner.
While the chain tensioner of the present invention is described in
relation to a packaging machine for beverage containers, the
invention is applicable to any process equipment using an endless
chain. The invention is also applicable to tension belts or other
endless devices on machines.
Referring to FIG. 1, a typical packaging machine 10 has numerous
conveyors for moving packaging materials such as cartons 11 and
articles to be packaged such as bottles 12. An infeed conveyor 13
feeds bottles 12 into machine 10. One or more conveyors 14 moves
bottles 12 through the machine where they are grouped and spaced to
be joined with cartons 11. One or more conveyors 15 moves cartons
11 from a carton magazine 16 through a portion of machine 10 which
erects cartons 11 and into an overhead carton carrier 17 which
carries cartons 11 and places them onto grouped bottles 18. An
output conveyor 19 moves the packaged articles 20 out of machine 10
to an area where they are consolidated for shipping. All of the
above conveyors on machine 10 can use a chain tensioner of the
present invention. The subsequent discussion of the chain tensioner
of the present invention is for one embodiment of it as used on the
overhead carton carrier 17, and for another embodiment used on a
conveyor 14.
The functioning of overhead carton carrier 17 and the packaging
machine 10 on which it is used is disclosed in U.S. Pat. No.
5,626,002 issued on May 6, 1997. Said patent being assigned to
Riverwood International Corporation, the assignee of this
application. The above patent is hereby incorporated by
reference.
Referring to FIGS. 2-4, an example of the preferred embodiment of
the present invention is illustrated and generally indicated by the
reference numeral 30. Overhead carton carrier 17 has a pair of
endless chains 25 running on sprockets 26 and 27. Carton carrier
assemblies 28 are attached to endless chains 25 at specific
intervals along chains 25. For overhead carton carrier 17 to
operate properly, proper tension in chains 25 must be maintained.
If chains 25 are too loose, carrier assemblies may not be properly
positioned and they may sway excessively. If chains 25 are too
tight, chains 25 may wear excessively and have to be replaced too
soon.
To maintain tension on chains 25, sprockets 26 and 27 are forced
apart by chain tensioning mechanism 30. Sprockets 27 are supported
by shaft 31 running in bearings 32 and 33 which are mounted on
slide assemblies 34 and 35 attached to frame 70 of machine 10.
Slide assembly 34 include linear guide rails 36 and 37 on which
linear bearings 38, 39, 40 and 41 slide. Base plate 42 is attached
to linear bearings 38 and 40 and base plate 43 is attached to
linear bearings 39 and 41. Bearing 32 is fastened to base plate 42
and bearing 33 is fastened to base plate 43 by bolts 48. Base
plates 42 and 43 have follower mount portions 44 and 45
respectively, to which followers 46 and 47 are rotatably attached.
These slide assemblies 34 and 35 allow sprockets 27 to be moved
linearly with respect to sprockets 26 to maintain proper tension in
chains 25.
Sprockets 27 are moved linearly by means of two snail cams 52 and
53 attached to shaft 51 by collars 54. Snail cams 52 and 53 push
against followers 46 and 47 respectively so that as shaft 51
rotates in the direction indicated by arrow A, the outer radius of
snail cams 52 and 53 at followers 46 and 47 increases, thereby
moving sprockets 27 away from shaft 51 in the direction indicated
by arrow B, which increases the distance between sprockets 26 and
27 and increases tension in chains 25.
A number of mechanisms are employed to rotate shaft 51. Frame
members 72 and 73 support shaft 51 which passes through and engages
a ratchet box 55 having a direction selecting lever 56. Ratchet box
55 is fixedly attached to frame member 74 and direction selecting
lever 56 is normally set to keep shaft 51 and snail cams 52 and 53
from rotating in a direction opposite of arrow A. A one way clutch
57 is attached to shaft 51 and a pearshaped lever arm 58 is
attached to one way clutch 57. End 59 of arm 58 is connected to the
piston 61 of an pneumatic cylinder 60 through rod end 62. Pneumatic
cylinder 60 is pivotably attached to frame 70 through mounting
bracket 63 and pivot member 64. Cylinder 60 may alternatively be a
hydraulic cylinder.
Pneumatic cylinder 60 is preferably a single-acting type. As
pneumatic cylinder 60 is pressurized to a predetermined amount,
piston 61 extends from pneumatic cylinder 60 and pushes end 59 of
arm 58 in the direction indicated by arrow C. Arm 58 and one way
clutch 57 are thereby rotated in the direction indicated by arrow
A. One way clutch 57 is oriented to grip shaft 51 when rotated in
direction A, and freely rotate on shaft 51 when rotated in the
opposite direction. Therefore, as one way clutch 57 rotates in
direction A, shaft 51 and snail cams 52 and 53 also rotate in that
direction to move sprockets 27 in the direction indicated by arrow
B to increase tension on chains 25. If shaft 51 rotates enough for
ratchet box 55 to advance at least another notch, then when
pressure is released from pneumatic cylinder 60, shaft 51 and snail
cams 52 and 53 will remain rotationally advanced in direction A the
amount that the mechanism in ratchet box 55 advanced. Chains 25
will thereby be incrementally tensioned by ratchet increments of
ratchet box 55. If shaft 51 does not rotate enough for ratchet box
55 to advance at least one notch when pneumatic cylinder 60 is
pressurized to a predetermined amount, then when pressure is
released from pneumatic cylinder 60, shaft 51 and snail cams 52 and
53 will rotate back to the position they were in before pneumatic
cylinder 60 was pressurized, and the tension in chains 25 will
remain the same as they were before pneumatic cylinder 60 was
pressurized. One way clutch 57 allows linear motion of pneumatic
cylinder 60 to rotationally advance shaft 51 through incremental
advancement of ratchet box 55.
Referring to FIG. 5, ratchet box 55 includes a housing 80, gear 81,
latch levers 82 and 83, springs 84, and 85, and direction selecting
lever 56. Housing 80 is attached to frame member 72 by mechanical
fasteners passing through apertures 86. Gear 81 rotates within
housing 80 and receives shaft 51 through aperture 87. Shaft 51 is
rotationally fixed to gear 81 by a key received in keyway 88.
The position of direction selecting lever 56 determines the
direction gear 81 will be allowed to turn. Direction selecting
lever 56 pivots on pivot 89 and has two lobes 90 and 91 which
engage latch levers 82 and 83 respectively. When direction
selecting lever 56 is moved to the forward position, lobe 90 pushes
latch lever 82 out of engagement with teeth 92 of gear 81 and lobe
91 allows spring 85 to push latch lever 83 into engagement with
teeth 92 of gear 81. Gear 81 can then rotate in the forward
direction with latch lever 83 riding over teeth 92, but if gear 81
is rotated in the reverse direction, latch lever 83 engages one of
teeth 92 to prevent rotation in that direction. When direction
selecting lever 56 is moved to the reverse position, lobe 91 pushes
latch lever 83 out of engagement with teeth 92 of gear 81 and lobe
90 allows spring 84 to push latch lever 82 into engagement with
teeth 92 of gear 81. Gear 81 can then rotate in the reverse
direction with latch lever 82 riding over teeth 92, but if gear 81
is rotated in the forward direction, latch lever 83 engages one of
teeth 92 to prevent rotation in that direction. When direction
selecting lever is midway between forward and reverse positions as
shown in FIG. 5, both latch levers 82 and 83 engage teeth 92 and
gear 81 is prevented from rotating in either direction. Direction
selecting lever 56 may be connected to an actuator so that
direction selection can be done remotely.
The chain tensioner can be activated at the beginning of each run
of a machine, by pressurizing pneumatic cylinder 60 to the
predetermined amount. If chains 25 are too loose, pressurization of
pneumatic cylinder 60 will advance ratchet box 55 at least one
tooth 92 and increase tension in chains 25. If chain tension is
adequate, pressurization of pneumatic cylinder 60 will not be
enough to advance ratchet box 55 one tooth, and tension in chains
25 will remain the same. Tensioning chains is thereby a
semi-automatic operation requiring a machine operator to only
activate the pneumatic cylinder. The system then sets proper
tension in the chain.
With a chain tensioner of the present invention, the amount of
incremental increase in chain tension is determined by the pitch of
snail cams 52 and 53 and the amount gear 81 needs to rotate in
ratchet box 55 to advance one tooth 92. The amount of force
necessary to advance ratchet box one tooth is a function of the
pressure in pneumatic cylinder 60 being counteracted by the tension
in chains 25. If pressure in pneumatic cylinder 60 is too high, the
ratchet box 55 may be advanced at a high chain tension resulting in
premature stretch and wear on chains 25 and a shortened working
life. If pressure in pneumatic cylinder 60 is too low, ratchet box
may not advance at a low chain tension resulting in sloppy chains.
By properly setting the pressure in pneumatic cylinder 60, proper
tensioning of chains 25 can be obtained.
To prevent chains 25 from being stretched beyond their useful
design limit by chain tensioner 30, a sensor 65, such as an
inductive proximity sensor is positioned to detect the end 49 of
plate 42. The sensing range of sensor 65 is such that normally
sensor 65 does not detect the presence of end 49. As chains 25 are
stretched, plate 42 moves closer to sensor 65. Sensor 65 is
positioned so that when chains 25 have been stretched a
predetermined amount by chain tensioner 30, end 49 of plate 42
enters the sensing range of sensor 65, which then sends a signal to
a machine controller to indicate that chains 25 have been stretched
to their maximum, and need to be replaced. Sensor 65 may be
electrically connected to a machine controller so that it activates
a switch to stop machine 10 and prevent it from operating until
chains 25 are replaced. Such a device prevents damage which can
occur if chains 25 would fail during operation of machine 10.
The embodiment illustrated by chain tensioner 30 is for relatively
large sprockets 27 and chains 25 requiring a fairly high tension.
For a smaller sprocket and chain requiring smaller tension, another
more compact embodiment as illustrated in FIGS. 6 and 7, is
suitable.
Referring to FIGS. 6 and 7, chain tensioner 130 is used on a
conveyor 14 of machine 10. Sprockets 127 are supported by shaft 131
running in bearings 132 attached to plates 142. The slider and cam
mechanism on the opposite side of sprocket 127 is not shown, but it
is identical to that shown in front of sprocket 127.
Plate 142 is attached to linear bearing 138 which slides on guide
rail 136 fastened to frame member 170. Frame member 170 has a slot
143 to accommodate shaft 131 which extends beyond plate 142.
Follower 146 is rotatably attached to bearing 132 and plate 142 by
bolt 148. Sprocket 127 is moved linearly by means of snail cam 152
attached to shaft 151. Snail cam 152 pushes against follower 146 to
move sprocket 127 away from shaft 151 in the direction indicated by
arrow E as shaft 151 and snail cam 152 rotate in the direction
indicated by arrow D, thereby increasing tension in chain 125.
Frame member 70 supports shaft 151 which passes through and engages
a ratchet box 155. Ratchet box 155 is fixedly attached to frame
member 70 and normally set to keep shaft 151 and snail cam 152 from
rotating in a direction opposite of arrow D. A one way clutch 157
is attached to shaft 151 and a pear-shaped lever arm 158 is
attached to one way clutch 157. In this embodiment, one way clutch
157 is small enough to fit within lever arm 158 and may be held in
place by set screws 153 or other fastening means. Collar 163
attaches to shaft 151. End 159 of arm 158 is connected to the
piston 161 of an pneumatic cylinder 160 through rod end 162.
Pneumatic cylinder 160 is pivotably attached to frame member
170.
Operation of chain tensioner 130 is the same as that of chain
tensioner 30. Pressurizing pneumatic cylinder 160 pushes end 159 of
arm 158 in the direction indicated by arrow F. Arm 158 and one way
clutch 157 are thereby rotated in the direction indicated by arrow
D. One way clutch 157 grips shaft 51, and snail cam 152 rotates in
that direction to move sprocket 127 in the direction indicated by
arrow E to increase tension on chain 125. If shaft 151 rotates
enough for ratchet box 155 to advance at least another notch, then
when pressure is released from pneumatic cylinder 160, shaft 151
and snail cam 152 will remain rotationally advanced in direction D
by the amount that the mechanism in ratchet box 155 advanced. Chain
125 will thereby be incrementally tensioned by ratchet increments
of ratchet box 155. If shaft 151 does not rotate enough for ratchet
box to advance at least one notch when pneumatic cylinder 160 is
pressurized to a predetermined amount, then when pressure is
released from pneumatic cylinder 160, shaft 151 and snail cam 52
will rotate back to the position they were in before pneumatic
cylinder 160 was pressurized, and the tension in chain 125 will
remain the same as it was before pneumatic cylinder 160 was
pressurized.
Sensor 165, preferably an inductive proximity sensor, is mounted in
frame member 170 and oriented and positioned to normally detect the
presence of plate 142. When chain 125 had been stretched a
predetermined amount, end 149 plate 142 will pass out of the
sensing range of sensor 165, thereby causing sensor 165 to change
its state, which can stop machine 10 until chain 125 has been
replaced.
For a chain tensioner of the present invention, it is desirable to
position the cams and followers relative to the sprockets they move
so that bending in the shafts supporting the sprockets and cams is
minimized. In a configuration where the sprocket support shaft is
short and the bearings and slider mechanisms are sufficiently
stiff, or where only one endless chain is used, it may be possible
to use only one cam and follower to provide chain tension without
causing excessive shaft bending. An arrangement that locates a
single cam and follower near the center of a longer sprocket shaft
may also be employed to provide chain tension with acceptable shaft
bending.
The descriptions above and the accompanying drawings should be
interpreted in the illustrative and not the limited sense. While
the invention has been disclosed in connection with the preferred
embodiment or embodiments thereof, it should be understood that
there may be other embodiments which fall within the scope of the
invention as defined by the following claims. Where a claim is
expressed as a means or step for performing a specified function it
is intended that such claim be construed to cover the corresponding
structure, material, or acts described in the specification and
equivalents thereof, including both structural equivalents and
equivalent structures.
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